Three studies are proposed to examine the role of peer groups in children s academic motivation and achievement. Peer groups are assumed to represent a powerful influence on children s adaptation, success, and well-being in school, but methodological problems of how to capture their influences have impeded empirical investigations. A method of Composite Social Mapping will be used to identify children s peer group networks in classrooms and to describe their psychological profiles. Study 1 extends two pilot studies on 4th graders and adolescents, using existing longitudinal (Fall and Spring) peer group data of an entire cohort of 6th grades (n=333), and teacher-and student- reports on their engagement in school. Processes of group selection (and homogeneity) are examined via correlations between children s individual scores and their groups aggregated profiles, and with multiple regressions, using individuals scores to predict changes in group profiles that are due to membership changes. Socialization analyses center on predicting changes in children s own engagement over time from their earlier peer group profiles. Subgroup analyses examine differences across gender, stable vs. unstable groups, and in-vs. out-movers. Study 2 aims to extend these findings (1) longitudinally from 4th to 6th grade, (2) to achievement outcomes of learning processes, and (3) to pathways from engagement to achievement via peer selection and socialization of engagement. Students grades and achievement scores in grades four and six are included in the existing data, as well as longitudinal measurements across grades (n=80). Analyses examine whether selection leads children s peer groups to remain homogeneous across the years (despite membership changes), whether socialization influences on motivation and achievement exist across grades, and whether links exist from peer influences on engagement to influences on achievement. Path analyses examine the extent to which children s achievement can be predicted across time for their groups socializing influences on engagement. Study 3 aims to support interpretations of these correlational findings in terms of peer socialization processes. It examines everyday social interactions in one 5th grade classroom, and aims to replicate a pilot study that focused on peer and teacher contingencies for students engaged and disaffected classroom behavior as one possible mechanism of peer socialization. Across 15 days, trained observers will observe target students behaviors and partners behavior consequences in the natural sequence of their occurrence. It is expected that highly engaged children will experience positive peer group contingencies following their on-task behavior, while disaffected children will receive negative non-group contingencies following their off-task behavior.